fox1976.pdf

Forest Ecology and Management, 1 (1976) 37--65 37 Elsevier Scientific Publishing Company, Amsterdam -- Printed in The Netherlands

CONSTRAINTS ON THE NATURAL REGENERATION OF TROPICAL MOIST FOREST

J.E.D. FOX

Biology Department, W.A. Institute of Technology, Bentley, W.A. 6102 (Australia)

(Received 1 July 1976)

ABSTRACT

Fox, J.E.D., 1976. Constraints on the natural regeneration of tropical moist forest. Forest Ecol. Manage., 1 : 37--65.

This paper reviews natural regeneration in tropical rain forests in terms of constraints. A potential for regeneration normally exists and silvicultural intervention should ideally take account of natural succession. Success is more likely with forests tending to single dominance or when the desirable crop species grow rapidly in response to light. Natural regeneration systems are currently unfashionable but are suggested as often being still the most appropriate methods of regenerating tropical forests. The forests are vulnerable to fire and as they contract in size animal populations exert increased stress. Providing biological rhythms are accounted for there seem to be few constraints to crop replacement. Exploitation of the forests often damages regeneration when logging is uncontrolled. This suggests more logging control is necessary to increase the availability of silvicultural options. Examples of seedling persistence, felling rules and silvicultural decisions are given for the dipterocarp forests of Sabah.

INTRODUCTION

Natural regeneration encompasses attempts by foresters to improve on nature by refining species composit ion, enhancing growth and maximising volume per unit area of valuable species. The general objective is to ensure that exploited crops are replaced, usually with trees of species characterising the natural forest. This paper deals with constraints to achieving natural regeneration (N.R.) in tropical rain forests as defined by Heinsdijk {1960). Factors influencing the objectives of N.R. are outl ined and the present status of the art is discussed.

The zone of tropical rain forest supports high forest and under a variety of condit ions the climax is reasserted fol lowing man's intervention. Woody trees will grow without man planting them and, over a period of time, the forest will tend to resemble that which existed prior to exploitation. Removal of t imber varies from 'creaming' (i.e. depletion) to a more or less clear felling, depending on relative frequencies and values of the larger species. Baur (1964) has stressed the comparat ively short history of attempts at N.R. in rain forests. F rom 1910 improvement fellings were made in Malaya and on

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a small scale in Andaman Islands from 1911 (C.C.F., 1968). These latter were of little significance. Generally the pattern of exploitation has followed an initial removal of valuable trees from easily accessible areas. Later stages have seen more concentrated fellings as more species have become marketable. The Tropical Shelterwood System (T.S.S.) was commenced during the second war in Nigeria and after the war the Malayan Uniform System (M.U.S.) was adopted in what is now Malaysia.

The techniques referred to as systems involve either attempts at inducing fresh regeneration or of tending existing advance growth. The systems involve intervention of one kind or another but not planting of replacement trees. Systems using N.R. are thus a compromise between no action at all following exploitation and the intensive activity necessary to establish a plantation (artificial regeneration) on land once carrying a complex rain forest. The simplest method of N.R. involves no treatment at all other than protection of the forest area between harvest visits.

"By and large throughout the tropics these systems have been abandoned because of lack of success." (Adeyoju, 1974). This sweeping generalization covers a multitude of problems. How do we define success? At what point in time can it be said that a crop has failed? Can precise causes be assigned to failure?

Fig. 1. Erosion following logging on soft sandstone at Segaliud-Lokan Forest Reserve, Sabah. Repeated passage of heavy crawler tractors up and down this slope exposed loose, soft, sandstone of the C horizon. Torrential rainstorms quickly erode this type of material. Prevent ion - - avoid logging up slopes on this soil type.

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Fig.2. Ponding up following blocking of natural drainage at Deramakot Forest Reserve, Sabah. Extraction of logs across a small stream resulted in water level rising and death of all remaining woody vegetation. Cure - - opening up of drainage. Prevent ion - - adequate use of culverts.

The criteria for success must clearly be weighted by economic considerations. Adequate accounting of expenditure in relation to quantified production should be a general management aim. Nigeria abandoned the formal T.S.S. operations in 1962 but the reasons had little to do with success per se. Lowe (1975) gives inter alia: independence, pressure for land, and change of emphasis to agri-silviculture as contributing to abandonment of the T.S.S.

The ecological basis for rainforest management has been frequently stressed (Baur, 1964; Fox, 1972; Whitmore, 1975) and is becoming more widely understood. Problem areas which need examination for each forest area are

(1) What can be done to influence quantity of regeneration? (2) How can species representation be restricted without losing other values

associated with diversity? (3) What time scales are appropriate to regeneration cycles? Working of the forest may reduce the potential for further yield by mal-

practice such as mechanical compaction of soil, silviculturally induced degradation, man-induced erosion (Fig.l) and excessive or insufficient drainage (Fig.2). Changes may then entail high levels of re-investment (Dawkins, 1972)

Constraints to the possibility of successful natural regeneration by silvicul-

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tural systems may be grouped as environmental, intrinsic (or biological) and of human origin. These are examined in turn, following a discussion of economic considerations. The paper concludes with a treatment of appropriate silvicultural systems and prospects for these systems.

ECONOMIC CONSIDERATIONS

N.R. is often said to be uneconomic on two main counts. Firstly low productivity per unit of land area. Experts show unbounded enthusiasm for plantations: "with high yielding crops grown on short rotations it becomes profitable to apply methods used in agriculture . . . . forests in Indonesia managed on the selection system rarely produce more than 1 m3/ ha/annum. Pure stands of high yielding species on the same site can produce 10--30 m3. '' (Lundqvist, 1964; see also Lowe, 1975). The second charge is that silvicultural operations are costly in terms of return for expenditure. When the major species regenerate freely without particular attention (Walker, 1948) it is scarcely necessary to indulge in much intervention. Some of the now discredited systems involved a number of visits and substantial man days of effort -- the Nigerian T.S.S. being perhaps the worst offender (Baur, 1964; Ogbe, 1968).

The main cost advantage of concentrated plantations is that of land. Where land is plentiful pine plantations are likely to be a luxury and to have only theoretical advantages over N.R. systems. Silvicultural treatment of forests represents a rare opportunity to convert labour into capital assets (Wadsworth, 1974). Though considered expensive by planners (Shao and Thomas, 1969) silvicultural treatment enables a given unit of money to be more widely spread in N.R. operations. It is not correct that natural forest intervention is always uneconomic. Earl (1973) has drawn attention to discrepancies between net discounted revenue per unit of land vis-a-vis per unit of money. A given sum of money may yield a greater total return if spent on more hectares for a lower average return per hectare.

Natural regeneration may be absent or scarce due to lack of seed bearers, or because germination is poor, or because seedlings die. The circumstances of survival need elucidation for the species with which the silviculturist is concerned. Some approaches to management are mathematical -- based on stocking and presence of a positive stand table (Dawkins, 1958; Pierlot, 1966). Damage to smaller stems and loss of seed source may devalue such systems. We may define success in terms of quantity, quality and growth. That is adequate numbers of given species per unit area which grow at acceptable rates. Success will then vary along a scale (per unit area) from very high numbers of highly preferred species growing rapidly to few or no preferred species growing slowly, if at all. This scale illustrates the paradox faced by the silviculturist -- the best regeneration may require little further intervention, the worst may suggest a lot of intervention is required.

"Wood consuming industries prefer to use as few species as possible. The

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ideal is one type of wood that can be used for several purposes. Concentration on a few species makes the forester's work easier." (Lundqvist, 1964).

Conversion of natural forest involves ecological risks greater than the early selection fellings still in use in Amazonia. Most systems used in recent years (cf. the more or less "even aged" of Baur (1964) involve considerable reduction in species, up to two thirds in Puerto Rico (Wadsworth, 1974). Foresters are everywhere ignoring sustained yield and condoning the notion that high forests are the best places for plantations and not the wastelands, derived savannahs, and areas of shifting cultivation (Lowe, 1975), which conservation policies would suggest.

Despite apparent economic advantages of plantations it has yet to be shown that the spectacular conifers can be continued indefinitely without detriment to the site (Dawkins, 1958). Similarly reliable prescriptions to avoid serious biological problems with plantations are not available (Wadsworth, 1974).

Superior growth in plantations is reported for some species (Lowe, 1975) but in Sabah it is difficult to get a planted dipterocarp to equal natural growth (T.C. Liew, personal communication, 1975). Governments require facts on which to base judgements and with tree growth in natural regeneration the main problem is that of quantification. Some Nigerian figures (e.g. Bangbala and Oguntala, 1973) suggest that adequate stems are present for removal 15 years after logging, with good potential for further cycles. The T.S.S. may sometimes result in stands approximating a selection system (cf. Bell, 1971) and our notion of success may require modification. In much the same way fortuitous secondary stands of Endospermum peltatum* are harvested under a clear felling regime in Mindanao where the Dipterocarpaceae are managed under a selection system.

Decisions on cutting regimes and treatments must either proceed at an infinitely slow pace or follow the rather ad hoc style deprecated by Prasada (1965). Criticisms have been made by Bell (1972) of earlier systems used in Trinidad Mora excelsa forests which either favoured other species or sought conversion to pine but his recommended selection system to favour M. excelsa is based on a few plots only. Clearly we must accept a great deal of inspiration -- "the complete study of regeneration in tropical rain forest would exceed the limits of a human working lifetime." (Webb et al., 1972). There is much advantage in minimal expenditure on cultural operations and maximal expenditure on usage of species which come to dominate regrowth stands, at least in the early stages of management. Systems which seek to ignore the commercial use of the most abundant species will inevitably be expensive. The following is a general rule, probably of universal application: The more that comes off (or more disturbance) the further back in the process of succession is the stand placed.

*E. peltatum is an excellent matchwood, grows to 80 cm diameter and is said to reach 30 m height in 3--6 years (Generalao and Torrenueva, 1972).

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ENVIRONMENTAL CONSTRAINTS

Variables likely to affect regeneration have been defined by Philip (1967). Here consideration is given to light, water, soil, biotic factors and storms.

Light

The influence of gap size on competition and composition has been well documented (Walker, 1948; Baur, 1964). Death of a single tree or a minor windfall may allow insufficient light for pioneers* to grow. If seedlings of dominant species are lacking then seedlings of pioneers (trees or lianas) may become established. Cultivation or losses in exploitation accentuate this trend. The larger the gap in the canopy the more light that reaches the undergrowth and the more intense the competition. The most successful species are those that can respond rapidly to this light though all growth may be favoured by openings (Schulz, 1960).

Light is an environmental variable controllable to some extent by the silviculturist. Gaps in the natural forest stimulate growth of all species able to benefit. Schulz (1960) reported that of 30 primary species seedlings examined only one grew best in less than full sunlight (Ocotea rubra). Nicholson (1960) showed that seedlings of five species of Dipterocarpaceae benefited from some shade. Initially growth was better in 50% daylight than in darker or lighter conditions, but after about 18 months' growth was more rapid in full light. In a second experiment high soil temperature and low moisture limited growth in fully exposed conditions. Other work in Sabah suggests that over time competition effects result in fewer survivors of larger average size surviving in lighter conditions in the forest. Optimum development of Araucaria regeneration occurs under lower and more open canopy, this being a function of lower rainfall, steeper topography or disturbance (Havel, 1971).

Ormosia krugii is capable of carbon fixation at low light intensity but develops faster in higher light intensities (Edmiston, 1970). The related African Afrormosia elata shows best overall growth in partial shade (Ampofo and Lawson, 1972). As the major influence on light regime is exploitation and there is evidence of increased felling damage to larger seedlings, preo exploitation canopy opening is scarcely necessary where adequate seedling regeneration is present. In Sabah liana cutting prior to felling gives some additional light, but the justification for this operation is reduction of felling damage. Abundant liana growth following exploitation is difficult to control and must be tolerated until several years after felling. The more intensive the exploitation the fewer the possibilities for manipulation of light available to the silviculturist.

*It is more useful to talk of species as pioneers (= "nomad" , see Van Steenis, 1956), primary dominants and understorey components rather than stands as varied secondary stages.

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Water

"Pore space and soil moisture . . . . are considered by some students of tropical forest soils to be the main factors of ecological importance" (Schulz, 1960). The importance of both structure and drainage of soil in delineation of forest types is unquestionable. In natural conditions regeneration is likely to produce the same or similar species on soils affected by flooding, water- logging, impeded drainage, shallow soil -- factors which simplify the com- munity (Budowski, 1970). Man's intervention by way of exploitation is having increasingly evident local effects on forest soils and their drainage. Complete removal of vegetation is rare and confined to extraction routes (Fig.l) so the spectacular erosion of lighter soils in more seasonal forests is uncommon. Seedlings of Dipterocarpaceae are vulnerable to flooding and much Parashorea tomentella was eliminated during the 1967 flooding of the Kinabatangan River in Sabah.

Rollet (1962) discussed regeneration of the seasonal East Mekong forests where species of Dipterocarpus and Heritiera javanica are dominant. These forests are difficult to regenerate as seed matures before the wet season. The legume Pterocarpus dalbergiodes, favoured in the Andamans, is easier to deal with as germination is delayed. Undergrowth is cleared and the canopy lightened prior to February/March when seedfall is due; weeding during the rains is accompanied by further canopy lightening in June/July (C.C.F., 1968).

Soil

The soil surface micro-climate is important to regeneration at two crucial stages: germination and canopy opening. At germination survival probability is higher if adequate moisture is available and temperatures are equable. In the Dipterocarpaceae optimal temperatures for germination are 28--30C, initial moisture content of seed is 60% and they cannot survive at less than 35% (Tamari, 1975). The soil temperatures of clearings may be slightly higher but germination can occur on bare exposed soil, or in grass though survival is low in comparison with the humid forest floor at lower temperatures. Established seedlings are prone to die from scorch or severe wilting under open conditions in dry weather (Fox, 1972). At canopy opening high temperatures combined with low soil moisture can be very damaging. While it may be possible to avoid fellings in the hot parts of the dry season in strongly seasonal forests, dry spells in the less seasonal forests are not as predictable. Use of more expensive machinery capable of all weather work is putting pressure on those governments which exercise some control to permit continuous working. Soil disturbance accentuates the competitive ability of pioneers by removing established, rooted, plants and bringing seed to the surface, or allowing opportunities for fresh seed to germinate in bare soil. Where such species are considered desirables some mechanisation can be beneficial (Finol, 1975).

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Biotic factors

In N.R. systems entomological problems are of little importance compared with those of monocultures (Gray, 1974). Seedlings of Goupia and Vochysia suffer heavy mortality from leaf cutting ants (J.R. Palmer, personal communication, 1975), a feature of some importance as these species appear to regenerate well following selective extraction in Amazonia (Heinsdijk and De Miranda Bastos, 1965). Larger animals are becoming more important as forest areas contract. Tapir causes local damage by trampling in Belize (Johnson and Chaffey, 1973). In Borneo deer feed in grassy clearings preventing normal succession, and elephants are increasingly evident in some areas (Fox, 1972). Elephants have become a problem in Uganda (Johnstone, 1967). Loss of traditional migratory routes and increased agriculture around the forest led to the herds spending more time in the forest. Enrichment planting was abandoned in 1944 and early attempts at refining were discon- tinued in 1957. The elephants feed on saplings of preferred regeneration species and control appears to be culling combined with attempts at exclusion from young regrowth stands. Despite the heavy emphasis on the merits of multiple use forestry in temperate countries, there are few examples in tropical rain forest.

Many lianas when small are stimulated by cutting, whereas the successful larger ones can be readily eliminated a few years after felling. Similarly there is little to be gained from attempting to kill off young individuals of nomad tree species. Competition rapidly thins them out and where dense they will seldom regenerate themselves and primary species can survive (Fig.3). Im- provement in the sense of removing structural components believed to hinder growth (or survival) of regeneration has a place in the Sabah Selection System (S.S.S.) (Anonymous, 1972). Here lianas are cut ahead of exploitation to minimise falling damage and intermediate (pole) sizes of desirable species are marked for retention. Marking is also a feature of the Selective Logging System (S.L.S.) of the Philippines (Fox, 1967). In both cases the tenet of the M.U.S. is followed after logging in that weeds, shrubs, lianas and nomads are left alone to allow the climber tangle to be carried up. This principle may be of more universal relevance viz Lowe (1975) discussing the Nigerian experience, " . . . opening the canopy to release regeneration appeared to be silviculturally irreconcilable with preventing a devastating growth of weeds and climbers".

In situations where the favoured species are colonisers then more intensive utilisation of the primary stand (Earl, 1968) and eventually agri-silviculture will tend to be favoured. With adequate regeneration of the primary species total destruction of the primary forest is disadvantageous. Treatments to assist primary species regeneration will generally be of the improvement type. Here the processes of natural succession are not drastically altered but taken advantage of. Competition may be a biological constraint. When liana growth is so dense that regeneration is swamped it may result in death of the desired species.

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Fig.3. Seedlings of Dryobalanops lanceolata on an old tractor path, Kalabakan Forest Reserve, Sabah. Most of the trees in the background are pioneer species of Macaranga, Anthocephalus and Trema which entered the site after logging which occurred 15 years prior to the taking of the photograph. Large leafed herbaceous plants in the foreground are Zingiberaceae (wild gingers). The man is standing amongst smaller leaved seedlings of Dryobalanops which grew in after logging from residual seed trees of this species in the vicinity.

I t is not only diff icult to apply a un i fo rm technique over varied condit ions, but as uti l isation values change more "undes i rab les" become of value. Ogbe (1968) noted technological prob lems of a biological nature which affect prof i tabi l i ty, i.e. unmarketab le species, and prevalence of wide crowns. Both contr ibute to low yields per unit area.

Storms

The history of tropical forestry is too short to adequate ly account for areas prone to wind damage, but clearly if a propor t ion of the forest is to fall down periodical ly an alternative rat ionale to sustained yield is required. Brouard (1967) discusses cyclone damage in Maurit ius and makes the po int that to some extent the forests are adapted to the condit ions though considerat ions of stabi l i ty are impor tant with plantat ions. Hurr icane Hatt ie caused widespread destruct ion in Chiquibul F.R., Belize in 1961, which upset sustained yield. By 1970 regenerat ion in the devastated areas had become dense thickets 6 m high ( Johnson and Chaffey, 1973). L ightning has been described as one of

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the principal causes of mortality in tropical rain forest, particularly in peat swamp where group damage may cover 0.6 ha (Anderson, 1960). Dead patches are also found on ridge tops in dryland forest, but both lightning and wind (which is rarely strong in low latitudes) are of only localised importance.

Ceratopetalum apetalum (Cunoniaceae) is found in almost pure stands in rain forest areas of New South Wales. As a species it is generally less than 25 m height and 25 cm diameter (Francis and Chippendale, 1970). The trees are vulnerable to exposure and stands of this species are best managed under the selection system (Baur, 1964).

INTRINSIC CONSTRAINTS

Population structure

The forest differs in composition from place to place. General trends can be picked out but there are inevitably localised differences due to moisture or slope. Comparisons between different types of physiography are often meaningless -- conclusions concerning forest on a lowland gently undulating terrain must differ from those concerning forest where sharp ridges alternate with steep valleys. The latter will have two (or more) contrasting microhabitats which are intimately related, whereas in the former changes will be more gradual and not necessarily as a result of topography. Individual trees at maturity have survived an unknown series of events and may have occupied a succession of microhabitats during the period from seed to maturity. Chance and selection are involved in determining which tree stands where at maturity (Ashton, 1969). Heinsdijk and De Miranda Bastos (1965) suggest that occasional occurrences of one (or several) species with frequency such as to suggest pure formations are exceptions due to local conditions. Tendency to single species dominance is seldom shown on mesic sites in the South American forests (Schulz, 1960).

All preliminary studies attempt classification of the stands and such studies emphasize groups of related species. For example, Rollet (1963) describes the Congo (Brazzaville) forests as Meliaceae (mainly Entandrophagma spp.) forests with Leguminosae and Irvingiaceae. The families Sterculiaceae, Ulmaceae, Sapotaceae and Combretaceae (Terminalia superba) are frequent. Other families, notably Annonaceae, Ebenaceae, Tiliaceae and Olacaceae, are dominant in the understorey.

Savill (1973) describes the West African rain forest at its western extremity. In Sierra Leone the Leguminosae comprise one third to one half of all stems greater than 60 cm in diameter. Though Meliaceae are present they are scarce and as with the Congo there are changes in the semi-deciduous forests with decreases in the overall number of stems, genera of Caesalpiniaceae; fewer Sterculiaceae, increased representation of Mimosacea, Moraceae, Combretaceae (Terminalia spp.), Bombaceae and Euphorbiaceae.

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The South East Asian rain forests show general dominance of the Dipterocarpaceae. Though Leguminosae are present they only become important at the semi-deciduous end (Rollet, 1962). The South American studies (e.g. Heinsdijk, 1960; Schulz, 1960) have generally given all woody species over 25 or 35 cm diameter. The summary work on FAO's inventories (Heinsdijk and De Miranda Bastos, 1965) describes some 20 million ha with about 400 species over 25 cm from 47 families. In order of abundance these families were Leguminosae (e.g. Piptadenia and Sclerobium), Lecythidaceae (Eschweilera ), Sapotaceae (Pouteria ), Burseraceae (Protium ), Lauraceae (Ocotea, Aniba, Nectandra) and Rosaceae (Licania). Of the Leguminosae Schulz describes single dominance for Dicorynia guinanensis, Mora gonggrijpii, Eperua falcata and Dimorphandra conjugata -- all of the Caesalpiniaceae.

Spatial distribution of trees in the natural forests can give guidance to regeneration possibilities. Though at first sight species distribution appears random closer scrutiny suggests that aggregation is common (Heinsdijk, 1960). Examples given by Schulz (1960) viz. Ocotea sp. (Wanapisie), Qualea rosea, Vouacapoua americana, show some relationship with soil types, but in a number of cases aggregation reflects previous (or present) presence of a seed bearer in the vicinity. Continuous regeneration must occur if stands of sufficient size are taken. Species capable of reaching a reasonable size and reproducing frequently are discussed by Knight (1975); on the basis of size/frequency patterns some 17 species are suggested as being climax trees for his Panama study area.

Evanescence of seedlings is a feature affecting composition of natural regeneration. Relative abundance will vary over time. As few studies have dealt with long term population changes in the natural forest an example from Sabah is given. Twelve rectangular plots 1 X 4 m were assessed annually in Kabili-Sepilok F.R. from 1958--1970. Of the 405 Dipterocarpaceae seedlings present in 1958 106 were still alive in 1970 (Fox, 1973). Individuals of ten species were observed; numbers and distribution varied with death and recruitment. Percentage survivals by years after recruitment are given in Table I.

TABLE I

Seedling populat ions fol lowing recru i tment

Year of % survival (years after recru i tment)

Seedfall Recru i tment No. 1 2 3 5 7 9

1958 405 88 68 59 43 33 29 1960 1961 89 79 62 39 28 20 10 1961 1962 31 77 48 42 23 19 1963 1964 892 63 47 34 19 1968 1969 66 90

(Fox, 1973, Table 29)

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26

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Average stocking per hectare was 83,000 in 1958, fell to a low of 59,000 in 1963, rose to a maximum of 230,000 in 1964, then gradually fell again to 68,000 in 1970. These figures are well above the average for Sabah. Many seedlings first measured in 1958 must have originated in 1955, a year of heavy fruiting, but some could have been considerably older than 15 years in 1970. No dating methods are available and much longer observation periods are necessary to determine longevity of such seedlings. Not all large trees in the vicinity flowered at the same time; this is reflected in the pattern of species representation after recruitment (Table II).

TABLE II

Seedling populations by plots and species

Seedlings counted (Number of plots)

Species Year 1958 1961 1964 1970

Shoreaparvifolia 73(9) 42(9) 357(11) 21(9) S. argentifolia 2(2) 1(1) 194(10) 8(4) S. leptoclados 90(10) 68(10) 226(11) 56(10) S. macroptera 141(3) 111(5) 217(6) 119(6) S. acuminatissima 70(8) 129(10) 97(12) 61(12) All seedlings 405 345 1116 364

(Fox, 1972, p. 180)

The other five species were less abundant and shorter lived. Felling of this stand at different times could have resulted in regrowth of differing composition. Lowest numbers of seedlings were recorded in 1963 just prior to the heaviest recruitment from fruit fall. Species performance was as follows: S. parv i fo l ia - - short lived, only 2 survivors 1958--1970, one grew from 30--60 cm in height. S. a rgent i fo l ia - - average numbers low, tended to die out rapidly following widespread recruitment but survivors grew more rapidly in height than other species and may survive a long time. S. leptoc lados - - only recruited in 1964, seedlings persisted longer than S. parv ivo l ia .

S. macroptera - - localised in distribution, seedlings persistent (accounting for 75% of survivors 1958--1970), show consistent small increases in height. S. acuminat i ss ima - - large numbers recruited, most died out at less than 10 cm height. Pattern suggests different parent trees fruited at the different dates. S. wa l ton i i - - seedlings scarce but very persistent, eight survivors, the tallest being 55--65 cm height.

Which seedlings successfully outgrow others? Webb et al. (1972) suggest that movement upwards is not a question of intermittent regeneration but rather that individuals get away. Definite advantages are possessed by coppice

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Fig.4. A stem of Shorea parvifolia under intensive growth study in a regeneration t reatment plot at Kalabakan Forest Reserve, Sabah. Felling took place 15 years before the photograph was taken and the measured tree was either a sapling or a small seedling at that time.

and it is postulated here that the older the seedling the faster its growth on receiving light. While development over time is less under shade {cf Ampofo and Lawson, 1972) the effect of persistence is not known. Absence of seedlings is an impediment to regeneration; should the species required be present but at a competitive disadvantage vis-a-vis seedlings of other species it is possible that their presence could be a constraint. Seedlings with only cotyledons are in "suspended animation" (Edmiston, 1970). Survivors generally acquire more leaves hence, presumably, have stronger roots; con- versely young seedlings will grow well if they have good leaf numbers.

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Abundance and growth

Comparative numbers of individuals influence N.R. Schulz (1960) suggests "the most decisive criterion for an evaluation of the relative importance of a species in a given stand is the number of individuals which, by reaching a certain size, show that they have succeeded in overcoming the principal obstacles in the struggle for existence." The size of 25 cm diameter was selected. In my work I have found that 60 cm is a more useful general criterion.

There are disadvantages in insisting that trees must reach very large sizes before cropping. At present such trees often have premium values but it is likely that second cuts will always give smaller average sizes. The advantage of equal sized stems cannot be obtained with N.R. but a minimum size and a modest range may be attainable. Examination of the diameter class distribution of stems in undisturbed forest can give useful information on likely sizes at maturity, apparent growth rates with size and periodicity of recruitment (Heinsdijk and De Miranda Bastos, 1965). Generally tolerant species are found in smaller size classes and light demanding species are found in the larger (higher) classes. If the forest is comparatively low, species that never reach the upper storey when the larger species are present may occur as dominants (Heinsdijk, 1960).

It is the shade tolerant species which are likely to have balanced diameter class distributions -- trees that have grown slowly are unlikely to be very plastic (Rollet, 1969). Species which emerge above the general canopy level forming a scattered and irregular upper layer are found in most tropical rain forests. These may reach heights of 60--80 m and have large basal diameters. Examples of emergents are Goupia glabra (Celastraceae) in Surinam; Tieghemella heckelii (Sapotaceae) in Sierra Leone; Koompassia excelsa (Caesalpiniaceae} in Borneo and Bertholletia excelsa (Lecythidaceae) in the Amazon. These species are often scarce in the vicinity in intermediate sizes. Schulz (1960) suggests that G. glabra is a strong light demander whose presence indicates past disturbance. Koompassia excelsa would appear to fit this rule but the other two species have somewhat heavy seed. Heinsdijk and De Miranda Bastos (1965) note ofB. excelsa that it only develops in open spaces and rapidly grows to maturity.

A number of species of more common/widespread occurrence have individuals which may reach emergent size. In Sierra Leone these include Meliaceae (Entandrophragma spp., Lovoa trichilioides); legumes (Brachystegia leonensis, Piptadeniastrum africanum ); Ceiba pentandra (Bombacaceae) and Lophira alata (Ochnaceae). These species are generally fast growers though L. alata is variable (Savill and Fox, 1967). In Sabah large individuals of a number of the Shorea species have been recorded. Two categories may be distinguished -- those species with a small percentage of individuals as emergents and those with a higher percentage. The latter are of great potential interest not only as rapid growers but as species of persistence. Knight (1975) has reviewed the role of emergents, suggesting that growth rates must exceed

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those of canopy species. A pioneer species with similar habits is Eucalyptus deglupta found as a large tree on volcanic ash in New Britain. This comparatively easy to cultivate species is being grown throughout the tropics in formal plantations, as is Araucaria hunsteinii -- also found in patches as a large tree. Gray (1975), discussing the New Guinea Araucaria stands, agrees with Havel (1971) that despite appearances such stands are not even aged and there is continuous regeneration.

Successional status

Entrance into a stand has three stages: firstly seed availability, then germination, followed by seedling survival (Havel, 1971). The more aggressive, rapid-growing, short-lived species classed as colonisers come into gaps. Agathis macrophylla is one of the few tropical members of the genus to be grown successfully as a plantation species. This species regenerates freely into hurricane or felling gaps on Santa Cruz (Walker, 1948). Other species with winged seed, of great utility as regeneration species, are the West African Meliaceae and Terminalia spp.; Heritiera in both S.E. Asia and W. Africa. Some South American species with short lived seedlings which come in waves and have high mortality are Couratari spp., Qualea coerula, Cedrela odorata, Tabebuia serratifolia (Schulz, 1960). Stands showing a tendency to single species dominance have particular appeal (Baur, 1964) and often produce dense seedling crops, e.g. Ocotea rodiaei, Eperua spp., and Mora excelsa in Guyana (C.A. David, personal communication, 1975).

All of these are not colonisers in the sense of being pioneer species. They are normal components of the forest types in the sense used by Havel (1971) for Araucaria hunsteinii. The status of Pornetia pinnata said by Walker (1948) to be typical of "mature secondary forest" is similar and the major role of these is similar to the Dipterocarpaceae. That is presence as seedlings surviving until a favourable event occurs and normal members of the forest types. Regeneration of Mora excelsa in Trinidad is abundant, aggressive, tolerant of shade, cheap and easy to establish. It is also said to be an invasive species (Bell, 1972), but it is not a pioneer.

Silviculture is complicated where the forests are already in stages of succession. in the West African forests there may be more hard woods, e.g. "Lorsque les villageois coupent la for~t dense pour 5tablir leurs cultures ils laissent souvent de grands arbres ~ bois dur ou tr~s gros, difficiles ~ abattre, ou ~ bois difficile

brfiler". (Rollet, 1963) Elsewhere stands with softwooded pioneers will occur within areas being

worked over for a second or subsequent cut (Whitmore, 1975). Information on later stages of succession is scarce (Knight, 1975) but the earlier stages are becoming better known.

A number of Bornean species which are pioneers are also normal con- stituents of virgin forest on moist sites, e.g. Anthocephalus chinensis, Duabanga moluccana and Octomeles sumatrana. Succession may be understood in terms

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of shifting species balance between the groups. From disturbance there is a trend towards loss of pioneers and towards a steady state of stability and self- perpetuation of the primary dominants. Many species of trees may be represented as seedlings where no obvious seed bearers are close and large numbers of small seedling lianas may survive disturbance in greater proportions than tree seedlings (Rollet, 1969). Seeds of nomad species may be assumed to be present in rain forest soil continuously. Baur (1964) refers to Nigerian work by Keay which showed that ten of 14 tree species (with 93% of individuals) germinated were nomads. In a recent elegant study in Borneo, Liew {1973) demonstrated that 14 of 17 tree species (with 99% of individuals) which appeared within 5 months were of nomad species. There was a distinct scarcity of ungerminated seed of the primary forest species in the soil. Though the Bornean lianas are not well known botanically it is clear that those abundant after exploitation are not as frequent in the primary forest. The term nomad may be applied to, for example, Merremia borneensis (Convulvulaceae) and Mezoneuron sumatranum (Caesalpiniaceae) which behave as nomads.

We do not know for how long seed of the pioneer species remains viable in the soil (Whitmore, 1975). It would appear that the seed pool is continuously replenished via bat and bird excrement -- most nomads are prolific, early fruiters. The relative contribution to secondary regeneration in large gaps from the existing seed pool compared with fresh seed is also not known. Behaviour of nomad species in the natural forests (Knight, 1975) is altered drastically by exploitation which provides many more opportunities for such species to assert themselves.

Phenology

Phenological studies are essential pre-requisites to understanding the regeneration potential. In many species some flowering occurs each year but heavy gregarious flowering and heavy seed production is irregular. Schulz (1960) noted that Ocotea rubra was irregular, fruiting in alternate years. Frankie et al. (1974) demonstrated that of 92 canopy species in moist forest in Costa Rica at least 12 species were in fruit each month, with a peak period when 32 fruited. This pattern is probably widespread -- of 38 trees from 21 species studied by Tamari (1975) in Malaya at least one tree was observed in flower each month (except August), though quantities varied and many trees did not set fruit. Similarly Pereira and Pedroso (1972) present data for 57 species at Curua Una. Flowering and fruiting was recorded each month with minimum fruit in August/September and a peak in January/March.

Wycherley (1973) discussed evolutionary advantages of gregarious flowering and summarised evidence for environmental stimuli. Factors of importance are photoperiodism, release of water stress, cooling, accumulation of assimilates following high insolation and water stress during opposed phases of the pluvial and solar cycles. In the Dipterocarpaceae accumulation of assimilates may

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determine long term periodicity but the trigger could be water stress. Predic- tion of heavy fruiting is not possible with this family in rain forest, nor indeed with dominants from a number of other areas (cf. Heritiera utilis, Sierra Leone in: Savill and Fox, 1967). In drier forests there are more obvious correlations with climate and with some species (e.g. Triplochiton scleroxylon, Jones, 1974) it may be possible to forecast fruit production.

Loss of flowers and fruit during maturation is high. Seed borers are of particular importance but these are constant factors. Unseasonal heavy storms which damage flowers or blow off immature fruits may cause severe loss over wide areas during gregarious activity. Further depletion of fleshy fruit is caused by birds and ground animals, but no reports of severe loss have been noted. After fruitfall germination is rapid for many species. The Dipterocarpaceae germinate almost immediately on reaching the forest floor and are notoriously difficult to keep. Araucaria hunsteinii loses viability completely after 8 weeks (Havel, 1971). Though many legumes have seed which can be stored for nursery work, their germination under forest conditions may also be rapid, e.g. Mora excelsa germinates within 3 weeks of falling (Bell, 1971).

Autotoxicity

The theory of succession implies change exemplified by the principle that pioneer stages do not regenerate themselves but nurse later stages; for example the "infrequent reproducers" of Knight (1975) viz. Cecropia, Didymopanax, Sterculia, Trema. If favoured as regeneration species this group would possibly require cultivation (cf Finol, 1975). Moving from rain forest pioneers to species of drier tropical forests there is evidence for a number of species that regeneration does not succeed in the immediate vicinity of the parent tree. Acacia senegal for example cannot regenerate under its own shade (Obeid and Seif E1 Din, 1970); Shorea robusta establishes itself best beneath species other than itself (Troup, 1955). Toxic factors are discussed by Baur (1964) in relation to rain forest species. He suggests that Manilkara nitida may produce a substance lethal to its own seedlings and refers to Australian work suggesting litter from Backhousia angustifolia decreased germination of Araucaria cunninghamii.

The African species Chlorophora excelsa is notoriously difficult to raise in plantations. Wood and Chenery (1955) sought for evidence of toxic effects with no success but were not able to completely rule out this possibility. In an elegant series of experiments Webb et al. (1967) demonstrated that Grevillea robusta seed would germinate but not survive in the proximity of active rootlets of the same species. This Queensland species cannot be raised in dense seed beds and will not reproduce under itself. The precise factor responsible for toxicity was not determined but it would appear to be water transferable and associated with the rhizosphere. This work suggests a general rule: commercial production of non-gregarious species may be possible only

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in polycultures. If this assertion proves to have substance it may have some bearing on the apparent scarcity of regeneration of dominants in African rain forests (Richards, 1952), though in Sierra Leone regeneration appears to be largely of the same species as originally present (Fox, 1969a). J.R. Palmer (personal communication, 1975) suggests that successful Amazonian pioneer species frequently have toxins or ant associations rendering them less susceptible to leaf cutting ants.

Alternation does not appear likely with the S.E. Asian Dipterocarpaceae. These species often occur in groves of large trees and the densest seedling regeneration occurs near the parent trees. Nicholson found that Parashorea tomentella seedlings failed to develop when germinated in non forest soil (Fox, 1972). Absence of myorrhiza may explain this type of event.

HUMAN CONSTRAINTS

Mechanical logging

"Technical perfection in cutting and transportation equipment is, from the biological viewpoint, disastrous. The more effective bulldozers, paper pulp machines, power saws and logging lines are, the greater the setback to natural regeneration." (Jacobs, 1974a). The raison d'etre of N.R. is to secure a second crop following exploitation. If uncontrolled the passage of large machines through the forest does enormous damage to prospects for N.R. Operations which are labour intensive, without a great deal of mechanisation, e.g. Guyana (C.A. David, personal communication, 1975), put less stress on the forest. Whereas the same machinery used in the Pacific North West may be ideal for coniferous regeneration, which can seed into mineral soil, considerable care is required in rain forests to minimise damage when existing seedlings are relied on for regeneration. Ideally each geographical area requires its own methods and techniques of logging; the potential for environmental damage from logging by any method increases as the slope increases (Wellburn, 1975). C omm on features with uncontrolled heavy bulldozer extraction are: severely eroded slopes in hilly terrain (Liew, 1974); churning up of low-lying moist areas; and creation of artificial swamps by cutting off natural drainage (Fig.2). Poor planning may lead to large landing areas and re-entry into already worked areas where growth has commenced may be very damaging to regeneration.

Economic arguments are put forward to justify re-logging or advance logging of smaller sized stand components. Either may be biologically disastrous (Whitmore, 1975) though production of the proof may be tedious (Fox, 1969b).

Examples of resource depletion ('creaming') following uncontrolled exploitation in the Amazon are given by Heinsdijk and De Miranda Bastos (1965). Aniba duckei (Lauraceae), source of pay-rosa essential oil, is said to have been virtually eliminated from some 3.7 million ha; similarly Manilkara huberi

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(Sapotaceae) the latex of which is used for chewing gum. Two valuable commercial timber trees Cedrela odorata and Cordia goeldiana had been removed over large tracts. It is also widely suggested that Virola surinamensis has been largely eliminated in seedbearer sizes from the Amazonian varzea (J.R. Palmer, personal communication, 1975).

'Creaming' per se may not be as detrimental as many silviculturists have supposed despite the many disadvantages, e.g. poor control, patchy exploitation, retention of defectives and ease of theft (Rees, 1963; Bell, 1971). When a species of the natural forest has ceased to replace itself conditions must have changed. The vanishing species must have originated at an earlier stage due to an unusual occurrence of natural or biotic events (Dawkins, 1958).

Fire

Residual unexploited rain forests are refuges. Many forest peoples made little impression on the rain forests but there is considerable evidence that destruction this century has proceeded alarmingly. Shifting cultivation has affected much of the high forest of Africa and also New Guinea (Gillison, 1969), the Pacific Islands, much of S.E. Asia (Rollet, 1962) and latterly the Amazon (Lima, 1954; Glerum and Smit, 1962).

Fire is not a feature of the natural environment in the moist rain forests (Rollet, 1962) and when it does occur many dominant, primary species are eliminated, at least temporarily. An exceptional dry period in northern South America in the spring of 1926 resulted in extensive areas of coastal swamp and savannah being burnt (Schulz, 1960; Whitton, 1962). Similar fires followed drought in 1963/1964, also affecting some rain forests on sandy ridges (Bhadran, 1965). Forest types with accumulation of peaty material are particularly susceptible as are the coniferous forests which may need positive protection from adjacent cultivation.

I have seen the effects of fire in the following areas: Lowland Dipterocarp Sabah (Babanga F.R.) early 1969 Dryobalanops rappa Brunei Peat swamp (Seria) mid-1969 Dacrydium elatum Sabah (Sook Plain) late 1970 Mixed conifer New Guinea (W. of Mt. Hagen) late 1972

These occurred after long dry spells when the ground had dried out, and all suffered elimination of dominant species which may never return. Forest areas more susceptible to conversion into grasslands are those where exposed infertile soils coincide with low seasonal rainfall (Lima, 1954). In such cases the ecotone may be sharp (Haantjens et al., 1965) but complete fire pretection could eventually lead to a return of high forest (Taylor, 1962). Once fire is a feature then the timing of fire may affect which species are successful (Richards, 1952). Leguminous species appear to be favoured in the long run. Poorer sandy soils are slow to revegetate as nutrient retention is particularly poor after burning: here nodulated species have a competitive advantage and it may be this factor which explains the occurrence of Casuarina (Gymnostoma)

56

on isolated hilltops in Malesia prone to lightning. Such sites have similar species to coastal padang in Sabah (Fox, 1972). Fire has adverse effects on white sand forest areas in Guyana: scrub now occurs over large areas where fire is coupled with past creaming (C.A. David, personal communication, 1975). For Belize, Johnson and Chaffey (1973) report relatively abundant regeneration of Swietenia and Cedrela on areas burnt in the past. In general, however, fire is injurious to regeneration and should not be permitted in managed forests.

Manpower problems

Numerous examples exist of political indifference to the role of forests and to their satisfactory regeneration. Lack of controlled, orderly exploitation often gives high current profit but renders subsequent harvests more costly. When cutting is organised on a cycle too short for regrowth to reach exploi~- able sizes (Meijer, 1974) then future employment is jeopardised.

The breaching of potentially satisfactory regulations is often overlooked. Illegal cutting is common in Java (Jacobs, 1974b); undersized trees are taken from Nature Reserves and Catchment Areas in Sumatra (Jacobs, 1975); and timber smuggling persists in the Philippines (F.S. Pollisco, personal communication, 1975). Of Indonesia Meijer notes "Even a colonial government would never have dared to sell out so much of its timber resources to foreign lumber interests". The policy of sustained yield was tacitly abandoned in Sabah for short term political gain (Stephens, 1967) and it appears now that in that State "areas under natural regeneration are to be felled for wood chips then con- verted, partly, to monoculture plantations for the same end use" (Jacobs, 1975). Brazilian Amazonia, the last great refuge of the rain forest, is by all accounts an enormous uncontrolled mess. Prior to the advent of military rule in the ex-colonial African States political corruption was starting to affect the management of rain forests -- in some States the reserved forests may now be more secure.

The men employed in N.R. operations should be highly skilled in tree identification; they should be able to visualise the results of present action some 5--10 years hence. The work involves considerable mobility, self- reliance and a willingness to forego the glitter of urban life. Those groups of people who really "know" the forests often do not want steady employment or to be associated with those who would supervise them. Partly as a con- sequence the disease Sheffield blight is common: "Cultural operations can easily suffer from a native love of indiscriminate cutting and slashing that wastes time and money and lets in so much light to the forest floor that weeds and secondary growth are unduly benefited." (Walker, 1948).

It has been noted for Nigeria that the nature of the systems used caused difficulties in checking that the work was done properly (Lowe, 1975), and Baur (1964) quotes Nigerian data for undergrowth slashing removing 63 useful saplings per acre when 40 was considered full stocking. "Economic regeneration is frequently cut by labourers" (Ogbe, 1968).

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Urbanisation leads to the situation where the young go to the field; the successful move to the town; and the dedicated, efficient, field men are over- worked, overlooked and underpaid. Lack of care in selecting men and poorly trained supervisors may both contribute to the achievement of poor results.

The professionals are not exempt from criticism. Too much early work was done with no estimate of regenerative capacity (e.g. Rees, 1963), with arbitrary decisions on objectives (Bell, 1971) and unimaginative use of felling rules (Plumptre, 1972).

SILVICULTURAL SYSTEM

In the natural forest succession is occurring continuously. N.R. systems to be successful must be based on an understanding of what happens in succession. Uniform systems may concentrate on groups of species of similar status; selection systems may include species from pioneers to climax. We may note a general silvicultural theory of succession: that removal of crop trees should avoid initiation of primary succession. The complete exposure of soil along extraction paths may be unavoidable but fire often is avoidable. Budowski (1970) suggests that "late secondary" species tend to tolerance as seedlings becoming intolerant later. This characteristic is more likely to give rise to a self perpetuating assemblage, indeed it is descriptive of the Dipterocarpaceae. Species having these properties may be managed effectively if cropping holds succession within the range of secondary seres. Destructive factors which may set succession back to an early stage include: landslips, cutting, burning, grazing, cultivation, silting, flooding, gaseous exhalations, salting and drainage changes. Effects of these factors depend on their duration (long/ short), extent (total/partial), onset (sudden/gradual), occurrence (persistent/ accidental). Repetition and timing in relation to development may accentuate destructive effects. (Jacobs, 1974a)

Exploitation creates a range of seral stages. These are related not only to light and size (Schulz, 1960) but also to soil disturbance. Exploitation seres fall in a range between the two extremes of excellent regeneration and poor prospects:

Excellent Poor

Size of gap small large Light conditions optimal excessive Soil disturbance little great

Success depends on the levels appropriate to the species assemblage and these levels are difficult to quantify and to implement in formal rules.

Treatment may be considered as initiating succession (e.g. felling); avoiding it (planting); altering it (heavy treatment); or as assisting it (improvement). Where regeneration is not present arboricides have been used to open the

58

canopy and stimulate recruitment (Philip, 1967). This is an example of alteration and it is difficult to avoid the natural succession in which a mass of rapidly growing vegetation is stimulated. Recognition of the stimulus given to lianas and coppice shoots has led to a tendency to discard pre-exploitation treatment (Ogbe, 1968) and heavy treatments generally.

More effort has been expended on seeking successful N.R. of Shorea robusta than with any other species of the Dipterocarpaceae. Though found in drier, more seasonal climates than rain forest, it is worth brief consideration here. Troup (1955) described work to 1944, and Prasada (1965) more recently reviewed performance in Bihar. As with all Dipterocarpaceae the seed is short lived; though seeding annually, good crops occur every third year. A promising seed crop may be destroyed by an untimely storm or insect attack. If seedfall is prior to the monsoon germination is poor; regeneration is scarce where soil is hard due to fire or grazing and may fail due to excessive soil moisture. It has not been possible to induce regeneration by canopy manipulation or other treatment. Prasada concludes: "Regeneration and management practices used for this important species have resulted from theories based on assumptions, approximations and, at times, bare-faced guesswork. What is wanted is basic fundamental knowledge in a quantitative sense. The information already available should be used with caution." Clearly the criteria for success are contained in the review, we may accept that current practice will inevitably depend a great deal on observations, quantitative data will be useful and we may note that for tropical forests generally: "Where regeneration has been absent, the only successful treatments to induce it have been ground weeding with some kind of soil working and drastic canopy opening with complete, if temporary, soil exposure." (Dawkins, 1958).

In moister, less seasonal forests, some regeneration is normally present at the time of exploitation. If regeneration is poor in quantity two main options are available. The first is effective control of exploitation. This is not possible in situations of confused tenure, remote or otherwise inefficient administration and when, though the operation may be marginal, it provides needed timber or employment. The second is silvicultural intervention: while control can usually be shown to have direct, obvious benefits, justification for expenditure on silviculture is often more difficult to demonstrate. The following accounts pay particular attention to the Dipterocarp forests in Sabah.

Control of exploitation

Lack of control over exploitation is the main constraint today to achieving N.R. In perhaps the majority of countries foresters do not have sufficient countervailing power; enlightened concessionaires whose time span is indefinite are also rare. Rules must take account of the logging system, what species and sizes constitute commercial timber, and known (or inferred) behaviour of the primary species. The rules should preferably be simple, easy to comply with and intelligible to machine operators. Fees can be manipulated to en-

59

courage use of less favoured species (or sizes) or discourage cutting of trees whose retention may be material to regeneration success.

As felling and removal of the large trees has a profound effect on the forest, exploitation in Sabah is the main influence on selection of procedures. Rules are in effect (Anonymous, 1972) which specify that felling coupes must be worked over in sequence; tree marking to ensure removal is not favoured -- positive retention of potential seedbearers is required where seedling loss is high and can be predicted. Higher minimum felling limits are used in hill protection forests to reduce damage, and undersized trees marked for retention are to be avoided by felling and extraction crews. Tractor path intensity should be held to a minimum and provision exists for supervisory personnel to sample intensity when assessing regeneration. Penalties may be invoked for damage to undersized trees and for excessive soil disturbance. Once a coupe has been cleared of timber it should not be re-opened. Narrow strips of uncut forest are to be left along watercourses to minimise drainage interference, major crossings culverted, and the size of log storage areas held to a minimum. Seed trees may be retained near such landings. Fires are prohibited.

Silvicultural treatment

In many areas for a variety of reasons there is a dearth of knowledge. Many measurements have been accumulated but few detailed syntheses have resulted. We need to know the capacity of ecosystems for change; some cannot (or should not) be altered whereas others are amenable to alteration (UNESCO, 1972). Rain forest ecology does not advance very far with simple inspections of present condition. An understanding of what really happens takes time and must involve repeated observations at the same sites. One should not ignore the evidence of one's eyes or scorn the presentation of useful observations as averages, or other modes using simple arithmetic. The recent paper by Bell (1971) is an excellent example of lucidity. Options need to be retained due to the often still primitive marketing systems. Once-neglected species often become desirable and invalidate earlier attempts at their destruction. In this connection particular attention must be paid to the pioneers. Short lived species die off naturally, longer lived species may become commercial as preservation and transport methods improve.

Silvicultural treatment in Sabah takes account of the varied pattern of change following exploitation. The following general rule (Anonymous, 1972) is applied immediately after exploitation: Poison girdle all species not listed for the forest area of 30 cm diameter and over. Residual lianas to be cut, larger ones to be poisoned on lower exposed surface.

A series of options are available based on estimated stocking per unit area in quadrats of 2 X 2 m (i.e. maximum of 2500/ha). Seasonally flooded areas are not treated when stocking is less than 250. Option E is followed when this level is found on dry land.

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Opt ion A - - under or near favoured species of 30--60 cm diameter with good crowns omit treatment other than poisoning larger undesired trees and treating any lianas. Opt ion B - - when adequate regeneration present (i.e. > 750/ha of preferred species, or > 1250/ha of preferred, desirable and accepted species) follow general rule and poison all stems over 60 cm diameter. Relics to be left as seed trees near landings. Opt ion C - - as general rule but where especially fine groups of stems 10--30 cm are impeded ignore diameter limits and carry out a liberation treatment to favour the selected poles. Opt ion D - - in unlogged patches of forest with seedlings present the diameter limit for stems to be poisoned is lowered to include understorey species. Opt ion E - - on dry land with stocking less than 250/ha cut lianas and release any groups of impeded pole sized stems.

This system attempts to account for local differences in the nature of the residual stand. Use of earlier blanket rules left little to the judgement of the men and often resulted in poorer results. The system accepts that uniformity is not possible. In addition liana cutting and tree marking are prescribed prior to exploitation to minimise felling damage, and selective intervention (liana cutting, liberation, removal of impeders) may be undertaken some years after exploitation.

PROSPECTS FOR SYSTEMS BASED ON N.R.

The tropical rain forest is rich in biological relations, is delicately balanced and is a vulnerable kind of vegetation. These features tend to complicate our understanding. Ecological studies can provide a scientific basis for the exploitation of tropical vegetation and with the counsel of ecologists, forests may be exploited yet survive; misused land may be rehabilitated and disastrous investments may be avoided (Jacobs, 1974a). In relatively few areas are these sentiments accepted by those who govern. Temperate workers often have little idea of the political issues involved. Whereas in advanced countries highly sophisticated debate occurs over comparatively insignificant problem areas frequently the ecologist in the tropics is waving a lonely and often misunderstood flag. Many rain forest areas are being radically changed without any preliminary studies (Lima, 1954) and where studies have been undertaken they have tended to be short term, half-hearted attempts.

I.U.C.N. (1972) recently urged governments to recognise that manipulation of tropical rain forests be based "on ecological analysis and principles, and the application of methods that can result in sustained yield". The face of Africa has been changed so radically that authors refer to pockets of this or that kind of vegetation (e.g. Rollet, 1963). In all countries where roads are constructed as the first stage of economic development the populace rush to utilise new land for shifting cultivation. In Brazil "new villages arise like mushrooms and forests are being cut down at an alarming rate" (Glerum and Smit, 1962).

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In situations where some assessment precedes exploitation there is often hesitancy on the part of governments in applying the necessary rules over exploitation. A recent case which has received some international publicity is that of the Agathis obtusa stands on Erromango. These were described (Johnson, 1971) as generally having sufficient seedlings "to probably maintain the species in its present abundance". When exploitation commenced it was considered so destructive that there was no chance of regeneration and erosion was being encouraged (I.U.C.N., 1972).

The success of N.R. is jeopardized through lack of land tenure, inadequacy of the human resource, political factors, lack of control over exploitation and fire. Control of fire, overgrazing and of regeneration generally is not exercised in forest lands whose ownership is not organised. Much of the unreserved high forest in Africa has disappeared, and maintenance of existing reserves is becoming increasingly difficult in many countries. Effective reservation policies are required in the Amazon, in the larger Indonesian islands and in Papua New Guinea. The latter country reported (Department of Forests, Papua and New Guinea, 1968) two instances of the successful use of N.R. to the 9th Commonwealth Forestry Conference. By 1972 both areas had gone, one to fire (possibly for hunting), the other to squatters. At the time of writing, due to lack of secure land tenure, N.R. is nowhere practised in that State.

N.R. has fallen into disrepute in many tropical countries. It is generally felt that N.R. is unfashionable, uneconomic and unsuccessful. It is unfashionable partly because it is difficult to measure. The profusion of species requires diligent botanical study~ large tracts entail much physical movement simply to sample growth, and progress of regeneration must be examined over time. There are many easier tasks for both young scientists and capable supervisors in developing countries.

N.R. is considered uneconomic in comparison with plantations. Experts exhort tropical countries to abandon N.R. as a system, to grow monocultures of exotics and to simplify silvicultural practices accordingly (Jones, 1974; Lowe, 1975). Simultaneously lay public opinion in advanced temperate countries is urging governments to use natural systems, to grow mixed stands of native species and to simulate primeval woodlands.

N.R. is considered unsuccessful largely because it is difficult to explain time scales. Developing countries are understandably anxious to show in con- crete terms what progress they have achieved. Such countries do not find forest regeneration high on the list of their priorities. The leaders can more easily see and appreciate what is going on, for example, in a rubber plantation than a N.R. system (Ogbe, 1968). When combined with the direct financial advantage of abandoning sustained yield and increasing present cut it is little wonder that governments rush to take the experts' advice.

Two phases of interest in using artificial regeneration have been documented by Baur (1964). The first phase occurs early on when problems of managing mixed stands appear insurmountable (e.g. Walker, 1948). The second phase occurs much later when the demand for agricultural land forces a swing to

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more intensive timber production. A further phase may involve questioning the value of intensive plantations as environmental concerns flow over to the tropical countries.

Silvicultural systems for natural regeneration must be simple, flexible and readily understood. Much greater emphasis needs to be placed on acceptance of what grows. Where shifting cultivation is prevalent, plantation programs (agri- silviculture) should take priority.

REFERENCES

Adeyoju, S.K., 1974. Forest resources of Nigeria. Commonw. For. Rev., 53: 99--119. Ampofo, S.T. and Lawson, G.W., 1972. Growth of seedlings of Afrormosia elata in relation

to light intensity. J. Appl. Ecol., 9: 301--306. Anderson, J.A.R., 1960. Dead forest patches. Borneo Terr. For. Bull., 8: 13. Anonymous, 1972. Manual of Silviculture (Sabah) for Use in the Productive Forest Estate.

Sabah Forest Rec. No. 8, Govt. Printer, Kota Kinabalu. Ashton, P.S., 1969. Speciation among tropical forest trees: some deductions in the light of

recent evidence. In: R.H. Lowe-McConneU (Editor), Speciation in Tropical Environ- ments. Academic Press, London, pp. 155--196.

Bangbala, E.G. and Oguntala, A.B., 1973. Merchantable Yields and Stand Projection in Akure Natural High F.R., Western Nigeria. Res. Pap. (Forest Ser.) No. 21, Ibadan.

Baur, G.N., 1964. The Ecological Basis of Rainforest Management. For. Comm., New South Wales.

Bell, T.I.W., 1971. Management of the Trinidad Mora Forests with Special Reference to the Matura F.R. Govt. Printer, Trinidad.

Bell, T.I.W., 1972. The Trinidad mora forests: to fell or not to fell? Comm. For. Rev., 51: 123--131.

Bhadran, C.A.R., 1965. Introduction of Regular Forest Management with Special Reference to the Preparation of a First Working Plan for the Mapane Unit of the Forests of Surinam, F.A.O., E.P.T.A. Rep. No. 2071.

Brouard, N.R., 1967. Damage by Tropical Cyclones to Forest Plantations with Particular Reference to Mauritius. Govt. Printer, Port Louis.

Brouwers, M., 1965. Report to the Government of Cameroon on Land Use and Agricultural Development. F.A.O., E.P.T.A. Rep. No. 2062.

Budowski, G., 1970. The distinction between old secondary and climax species in tropical central American lowland forest. Trop. Ecol., 11: 44--48.

C.C.F., 1968. Forestry in Andaman Islands, Port Blair. Chief Conservator of Forests, Andaman and Nicobar Islands.

Dawkins, H.C., 1958. The Management of Natural Tropical High-Forest with Special Reference to Uganda. Imp. For. Inst. Pap. No. 34.

Dawkins, H.C., 1972. Forestry factory or habitat? Comm. For. Rev., 51: 327--335. Department of Forests (Papua and New Guinea), 1958. Progress Report 1960--65.

Govt. Printer, Port Moresby. Earl, D.E., 1968. Latest Techniques in the Treatment of Natural High Forest in South

Mengo District. Govt. Printer, Entebbe. Earl, D.E., 1973. Does forestry need a new ethos? Comm. For. Rev., 52: 82--89. Edmiston, J., 1970. Some autecological studies of Ormosia krugii. In: H.T. Odum and

R.F. Pigeon, (Editors), A Tropical Rain Forest. U.S.A.E.C., Oak Ridge, Tenn., pp. B291--29~ Finol, H., 1975. Metodos de Regeneracion Natural en Unos Tipos de Bosques Venezolanos.

Universidad de los Andes, Merida.

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Fox, J.E.D., 1967. Selective logging in the Philippine diptercarp forest. Malay. For., 30: 182--190.

Fox, J.E.D., 1969a. Natural Regeneration of the Kambui Hills of Sierra Leone. Thesis, University of Wales.

Fox, J.E.D., 1969b. Silvicultural and economic aspects of re-logging. Annu. Rep. Res. Branch, 1969, Forest Dept, Sandakan, Sabah, pp. 100--107.

Fox, J.E.D., 1972. Natural Vegetation of Sabah and Natural Regeneration of the Dipterocarp Forests. Thesis, University of Wales.

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